Learning Objective
Control an SG90 servo accurately and calibrate its useful positions for a real project.
Introduction to Motors: SG90 Servo
Hardware: SG90 Micro Servo Motor
Dashboard: Servo Motor Control Card
See How the SG90 Servo Works
Read the picture from left to right: the command → what happens inside → the result.
1 · What it receives
A repeating pulse that names the angle to go to.
2 · How it works
A motor turns gears while a part inside checks the angle (feedback). It stops and holds at the target angle.
3 · Why it matters
Exact angles let a project open, point or lift, not just spin.
Where might we use it?
- Parking barriers
- Robot arms
- Automatic vents
Student sentence: A servo uses a motor, gears and feedback to move to a chosen angle and hold it.
Teacher/parent prompt: Ask, “What goes in on the left, what happens inside, and how does it help someone?”
Theory: Precise Mechanical Motion
From Sensing to Movement
MakerBuddy has measured temperature, distance and motion. Now it can act on that information. A part that turns electricity into movement is an actuator. The SG90 servo is one: it moves a gate, pointer or flap to a chosen position.
Servo Motor vs. Ordinary DC Motor
A DC motor spins nonstop while powered and doesn't know its position. A positional servo receives a target angle, moves its shaft there and stops. The SG90 moves through about 0° to 180°.
How the SG90 Holds an Angle
Inside are a small motor, gears, a position sensor and a control circuit. MakerBuddy keeps sending the angle it wants. The servo turns until its shaft matches, then stops. This checking is called closed-loop control. If something nudges the horn, the servo tries to push it back to the angle.
Angles, Horns and Mechanical Limits
The plastic arm on the shaft is the servo horn. Every build is different: a cardboard gate might close at 15° and open at 105°. Calibration means testing the real mechanism and recording the safest useful angles. Never twist the horn by hand or force it past an obstacle: stuck (stalled) gears can buzz, draw extra current and get damaged.
Real-World Applications
Servos move robot arms, camera mounts and greenhouse vents. Later you'll use one in a parking gate.
For Teachers
Compare an input (the HC-SR04) with an output (the servo). Keep parts light, leave space around the horn and approach limits slowly. If a servo buzzes nonstop, gets warm or restarts the board, remove the obstruction and power down before checking.
For Parents
Your child is learning how digital commands become real movement, using a servo found in beginner robots. They also calibrate positions that work in a real build.
Try It: Calibrate a Servo Barrier
Interactive demo · no kit needed
Play with a pretend MakerBuddy board and its web page, right here.
Follow the steps one at a time. Got the kit? You can switch to the real board inside.
Hands-On Activity: Servo Positioning and Calibration
Activity Duration: 20-25 minutes
Connect the SG90, try some angles, then find safe open, middle and closed positions.
Step-by-Step Instructions:
- Inspect the Servo: Find the blue case, shaft, removable horn and three-wire lead. Give the horn room to move.
- Power Down First: Disconnect power before you attach or remove the servo.
- Connect the Servo: Plug the SG90 into the 3-pin connector marked 19 on the bottom edge. It fits only one way; never force it.
- Open the Dashboard: Clear the area around the servo, then plug the USB cable back in; the servo turns to 0°. Find the Servo Motor card; it shows 0 °.
- Center the Servo: Drag the Position (0° - 180°) slider to 90 and let the servo stop. For exact angles, click the slider and use the arrow keys (1° per press). With your teacher and the power disconnected, fit the horn so a pointer is roughly centered.
- Test Reference Angles: Plug the USB cable back in (the servo turns to 0° again) and press 🔌 Connect. Try 0°, 45°, 90°, 135° and 180°, pausing after each. Watch which way and how far it moves each time.
- Add a Lightweight Load: Attach a short cardboard pointer or barrier arm. Keep fingers and loose objects clear of the horn.
- Calibrate Useful Positions: Move in small steps to find a safe closed, middle and open angle. Stop before the arm hits anything.
- Record the Results: Write the three angles in a table. Test each one three times.
What Students Should Observe:
- The servo moves to an angle and stops; it doesn't keep spinning
- 90° is near the middle of the range
- The same command returns the horn to about the same spot
- The best open and closed angles may not be 0° and 180°
- A loaded servo may make a short sound while moving, but should never stay stuck or buzz nonstop
Servo Safety
Connect the servo only while the board is powered off. Use a light arm, keep fingers clear and never force the horn by hand. If it buzzes nonstop, stops against an obstacle or gets warm, return it to a safe angle and disconnect power.
Challenge
Your Mission: Build and Calibrate a Parking Barrier
Turn your servo into a mini parking barrier that opens and closes without hitting its frame.
Challenge 1: Find the Physical Limits
- Attach a short, light cardboard arm to the centered horn
- From 90°, move down in 5° steps until the arm is flat (horizontal)
- Record that as your closed angle
- Back at 90°, move up in 5° steps until the arm is vertical
- Record that as your open angle
- Test closed → open → closed five times and note any changes
Challenge 2: Improve the Motion
Make one improvement, like a robotics engineer:
- Move the horn so your angles stay away from the servo's end points
- Shorten or lighten the arm if the servo struggles
- Mark a middle position for testing and repairs
- Label your final closed, middle and open angles
Discussion Questions:
- Why might two groups need different angles with the same SG90?
- What happens if the barrier hits something first?
- Why does landing in the same place matter more than using all of 0° to 180°?
- Which sensor could spot a vehicle and open the barrier?
Bonus Challenge: On the Potentiometer Mapping card, select Servo, then turn the board's potentiometer knob to move the barrier. Only one mapping—LED, RGB or Servo—can be selected at a time. While Servo is selected, the Servo Motor card is locked and says “Potentiometer mapping owns the servo.” Choose None to use the slider again. After a power restart, select the mapping again.
Key Takeaways
✓ Servo Position Control
A positional servo moves to an angle and stops, unlike a DC motor, which keeps spinning.
✓ Closed-Loop Feedback
The servo compares its shaft position with the target angle and moves until they match.
✓ Mechanical Calibration
Dashboard angles are commands. Testing your real build finds the safe closed, middle and open angles.
✓ Sense-Decide-Act Systems
A sensor senses, logic decides and an actuator acts. An HC-SR04 plus a servo can make an automatic parking barrier.
Coming Up Next Week:
Week 15: Relay Control & Electrical Isolation — Use a low-voltage signal to safely switch a separate classroom load.
Learning Support
Use this quick guide to help every learner understand, practice and explain Introduction to Motors: SG90 Servo.
For students
Try it in three steps
- Say it: explain the main idea in one simple sentence.
- Show it: With the USB cable unplugged, connect the SG90 to connector 19. Position it at 0, 90 and 180 degrees.
- Stretch it: Determine physical limits and calibrate vertical/horizontal sweeps.
Checkpoint: What was your input, what decision or process happened, and what was the output?
For teachers & parents
Coach without taking over
- Before: ask the learner to predict what will happen and why.
- During: use prompts such as “What changed?” and “What could you test next?” instead of giving the answer.
- After: ask for a 30-second explanation, one piece of evidence and one improvement.
Look for: safe handling, correct vocabulary, a result the learner can demonstrate, and an explanation in their own words.
Did you get it?
Three quick questions. Pick an answer to see whether it is right, and why.
1How is a positional servo different from an ordinary DC motor?
2What does calibration mean for a servo gate?
3What should you do if a servo buzzes continuously against an obstacle?